Both Sultan and Darwish document how traditional Islamic law, or sharia, underpins Islamic life. Darwish argues that under Islam’s golden period of conquest and imperial rule, sharia’s most important aspect was “total control of the large and diverse Muslim empire—everyone’s behavior, loyalty, mind and even soul.” The system was all-encompassing and punishments were strict, but the caliphs, or rulers, were exempt from penalty for theft, adultery, killing, or drinking; in addition, they alone could have an unlimited number of wives. Their subjects were not allowed to revolt against them unless the caliphs acted in an “un-Islamic” way. Indeed, the fate of the learned imams who had written the sharia law demonstrated the extent of the caliphs’ immunity: they all wound up imprisoned, punished, exiled, or poisoned.

This system, Darwish writes, continues today in the tyrannical—and broadly accepted—behavior of most Muslim rulers. And the behavior cascades downward through Islamic society: those in positions of authority, whether in business or government, often act in repressive ways toward subordinates or the public at large. For many Islamic men, the home is the only place where they can assert their authority; yet even there, Darwish suggests, that authority is less than it seems. She analyzes the corrosive impact of polygamy, practiced or merely hypothetical, on all family members. She also notes its contribution to societal tension: since women do not greatly outnumber men, richer, older men acquire numerous wives at the expense of poorer young men. Caught between exclusion from a normal family life and brutal behavior in the public sphere, the best outlet for many young men is jihad: “The bottled-up sexual rage of the Muslim male,” Darwish argues, “must explode in the faces of the foreign infidel.” Jihad is thus essential for the maintenance of sharia law.

For her part, Sultan emphasizes the fear inherent in Islam, where the Koran’s 99 attributes of God include “The Harmer,” “The Compeller,” “The Imperious,” “The Humiliator,” and “The Bringer of Death.” She traces this to the dangerous environment of the Arabian desert, in which life was fragile and unpredictable, heightening people’s fear of the unknown. She also emphasizes the traditional Bedouin practice of raiding; Bedouins feared raids, yet relied on them for their own survival. Muslims today, too, are governed by the philosophy of raiding, she suggests...